The tracking of objects is used in many different industries ranging from military defense to computer assisted surgery. In the medical field, tracking systems have been utilized with medical devices to assist surgeons in performing precision surgery.
Typical configurations and methods for tracking objects are well known in the art. One such method exploits the emission or reflection of signals (light, radiofrequency, infrared) attached to an object, wherein the signals are detected by receivers (photodiodes, CMOS or CCD cameras). The signals are then processed to locate the position and orientation (POSE) of the object. Likewise, receivers may detect patterns, sequences, shapes, or characters attached to an object that may also be processed to determine the POSE of the object. In particular, optical tracking systems utilizing infrared or visible light are commonly used due to their accuracy and adaptability.
However, a common problem or limitation of such optical tracking systems is the need to maintain a line of sight (LOS) between the optical signals and the optical receivers. For example, when an object that is being the tracked is in motion, different orientations, positions or other objects may cause a disruption in the LOS between the optical signals and the optical receivers. Once the LOS is obstructed, the object can no longer be tracked. Other tracking systems have been developed to overcome the LOS problem. For example, electro-magnetic tracking systems (EMTS) can be used without the LOS limitation; however EMTS is not suitable in an operating room due to the potential electro-magnetic interference with other equipment and is currently less accurate than optical tracking systems. Similarly, accelerometers, and gyroscopes, known as inertial measurement units, can track objects however they intrinsically accumulate error in their position and orientation measurements over time.
Furthermore, when tracking objects in a surgical setting, there may be many instances in which the LOS becomes obstructed. For example, when operating a tracked tool, optical signals rigidly fixed thereto may be visible at one stage of the procedure but may become obstructed during a subsequent stage. This may be caused by the POSE of the tracked tool during operation. Additionally, fluids, operators, as well as other objects may also obstruct the view of the optical signals to the optical receivers. Generally, when the LOS is lost, the surgical procedure must be interrupted until the LOS is reestablished. Reestablishing the LOS currently requires manual adjustment of the optical receivers and/or optical signals. In the case of computer-assisted surgery, the manual adjustments may prolong a procedure and make it more difficult to achieve a desired surgical outcome.
During computer assisted surgery, fiducial marker arrays may be used to track rigid objects, including the operative anatomy, such as the femur. Generally, the optical tracking system has certain direction or image planes that provide the highest accuracy and/or obtain the best visibility. However, some procedures require large ranges of motion for the operative anatomy; in the case of total knee arthroplasty (TKA), the range of motion can be 120 degrees or more. During a knee replacement surgery, it is common for the surgeon to articulate the tibia and the femur throughout flexion and extension to determine how well the medial and lateral ligaments are balanced. The optical signals generally have limited fields of view, which may require the use of multi-face markers, which can require complicated registration algorithms and calibration of each face independently.
Additionally, with traditional tracking systems, the optical receivers are placed in a designated position in the operating room. The optical receivers are fixed relative to the tracked objects whereby any movement of the optical receivers during operation may require re-calibration and/or registration of the tracked objects relative to the new position of the optical receivers. Due to the fixed position of the optical receivers during the procedure, the tracked objects may move out of the tracking field of view. Therefore the LOS is lost between the tracked object and the tracking system causing an interruption in the procedure until the LOS is reestablished.
Further, the accuracy of the tracking system can depend on the field of view of the optical receivers. The field of view may be a function of the angular distance between the two optical receivers as well as the POSE of a collection of optical signals (a fiducial marker array) relative to the optical receivers. A larger convergent angle between the two optical receivers results in a smaller field of view and a more accurate system. Traditional tracking systems generally have two optical receivers that are fixed relative to one another. Therefore, the system is limited in optimizing the accuracy of the tracking system as the tracked object moves relative to the optical receivers. Similarly, if the optical signals are more aligned in the field of view of the optical receivers, the accuracy of the system is also increased. In conventional optical tracking, the fiducial marker arrays are generally fixed and remain static relative to the tracked object. Thus, the POSE of the object may change such that the optical signals are skewed away from an optimal field of view for tracking.
In the example of total knee arthroplasty (TKA), with respect to prior art FIG. 1 an operating room is illustratively shown with various components of a computer-assisted surgical system. Robots or computer assisted surgical devices 101 have an end effector 106, usually a drill or burr, for preparing the femur and tibia to receive an implant. The end effector 106 is tracked or navigated relative to the bone 112 using tracking arrays 107, 113 and an optical tracking system 108. Illustratively, the robot has various prismatic and revolute joints 102, 103 that provide control or motion in various degrees of freedom. A robot end effector flange 104 provides attachment for a tool 106 to be manipulated by the robot. Upon assembly of the tracking array 107 and end effector 106 prior to surgery, the POSE's of the coordinate systems are fixed relative to each other and stored in memory to accurately track the end effector during the surgery (see for example U.S. Patent Publication 20140039517 A1) relative to the bone anatomy 112.
A monitor 111 may be in communication with the hardware and software to provide a visual display for a user. The monitor may convey to the user various information that may include patient information, workflow instructions, real-time monitoring of the procedure, safety alarms, tracking information, as well as any other useful information and/or instructions that may be needed before, during, and/or after a procedure. Information may also be conveyed to the user via a heads up display unit or Google Glass™. A user may also interact with the robotic system 101 and/or tracking system 108 to provide input into the system(s). The monitor 111 may be a touch screen wherein a user can select and/or press different options, prompts and/or perform different actions. A remote control, joystick, mouse, keyboard, pendant and the like may also be wired or wirelessly connected to the systems to provide the interactive mechanism for the user.
A tracking system 108 with at least two optical receivers 109 may be in communication with tracking hardware 110 also shown in FIG. 1. The tracking hardware 110 may be a tracking computer, tracking controller and/or any additional storage device such as RAM, ROM, and/or other non-volatile memory. The tracking hardware may store, process and/or be programmed with various software applications, data and utilities that may include image processing, filtering, triangulation algorithms, registration algorithms, and coordinate transformation processing. The tracking hardware may be further configured to receive and/or execute input data from an external device either through a wired or wireless connection. Likewise, the tracking system 108 may be in communication with other devices in the operating workspace.
However, during TKA, multiple chamfer cuts are needed to prepare the femur and tibia. The chamfer cuts required requires the end effector 106 to be positioned and oriented in various POSE's to prepare the bone whereby the LOS of the tracking array 107 and the optical receivers 109 may become obstructed. For example, the end effector 106 and tracking array 107 may be aligned with the optical receivers 109 while preparing the anterior femoral chamfer cut, but to prepare the drill holes to receive the tibial implant, the end effector 106 and tracking array 107 are oriented 90 degrees from the chamfer cut. Therefore, the line of sight between the tracking array 107 and the optical receivers 109 is limited or lost and the user needs to manually adjust the optical receivers 109 for tracking. Similarly, considering that the operating room can be a crowded environment, other objects can interfere with the LOS for tracking.
While other types of tracking systems are contemplated that utilize other forms of energy such as electromagnetic fields and acoustic energy, these tracking systems may also be hindered by certain obstructions between the energy source and their respective receivers. For example, an electromagnetic fiducial marker emits a field of energy that needs to be received by the tracking system such that the POSE of the fiducial marker and/or fiducial marker array can be determined. Any electro-magnetic field interfering device or object that obstructs the communication to the receiver may affect the accuracy of the tracking.
Thus, there exists a need for a method and system that can utilize the accuracy and adaptability of an optical tracking system to track an object by maintaining a LOS between the optical signals and the optical receivers regardless of the position and orientation of the object being tracked. There further exists a need to reduce the possibility of other objects interfering with the LOS. There also exists a need for a method and system to provide continuous tracking of a computer-assisted or robotic device that decreases operating times, and improves surgical accuracy, without additional user requirements or adjustments to maintain the LOS of the optical tracking system.